Method of transporting natural gas

ABSTRACT

A METHOD OF TRANSPORTING NATURAL GAS INCLUDING THE STEPS OF TRANSPORTING BULK VOLUMES OF NATURAL GAS IN THE FORM OF A LOWER ALKYL AMINE TO APOINT REMOTE FROM A POINT OF ORIGINATION, DECOMPOSING THE LOWER ALKYL AMINE AT THE POINT OF DESTINATION TO METHANE, AMMONIA AND NITROGEN, AND THEN SEPARATING THE METHANE FOR UTILIZATION. THE LOWER ALKYL AMINE CAN BE THERMALLY DECOMPOSED, OR IT CAN BE DECOMPOSED BY CATALYTIC HYDROGENATION. THE NITROGEN CONTENT OF THE AMINE CAN BE RECYCLED ON THE RETURN TRIP OF THE TRANSPORTING VESSEL AS AQUEOUS AMMONIA FOR RE-USE, OR IT CAN BE USED AS A HYDROGEN SOURCE IN THE RECONVERSION OF THE AMINE TO NATURAL GAS.

United States Patent US. Cl. 4819() R 13 Claims ABSTRACT OF THE DISCLOSURE A method of transporting natural gas including the steps of transporting bulk volumes of natural gas in the form of a lower alkyl amine to a point remote from a point of origination, decomposing the lower alkyl amine at the point of destination to methane, ammonia and nitrogen, and then separating the methane for utilization. The lower alkyl amine can be thermally decomposed, or it can be decomposed by catalytic hydrogenation. The nitrogen content of the amine can be recycled on the return trip of the transporting vessel as aqueous ammonia for re-use, or it can be used as a hydrogen source in the reconversion of the amine to natural gas.

This invention relates to improved methods of transporting and/or storing natural gas.

Within defined boundaries, for example, within the United States, the transportation or movement of natural gas usually is by pipeline. Within such boundaries, this is generally a practical means of doing so. In recent years, however, the usage of natural gas in the United States has increased tremendously, while the available reserves have decreased. As a result, natural gas is being brought into the United States from distant natural gas producing areas to supplement the domestic supply. In most cases, it is completely impractical to move or transport this natural gas from these distant areas to the United States, by pipeline. It likewise is impractical to transport this natural gas in gaseous form, in view of the size of the transport carriers such as ships which would be required to handle the necessary volume of natural gas. If the natural gas is compressed, still additional problems arise.

Presently, the only method in commercial use for transporting natural gas from these distant areas is to liquefy the natural gas, ship it in specially built cryogenic tankers, and then re-vaporize the liquid natural gas (LNG) at the point of destination. This method has not achieved complete commercial acceptance, for numerous reasons, some of which are the high cost of the equipment required to liquefy the natural gas at the distant gas producing area, the high cost of the necessary specially built cryogenic tankers, the cost of storing as a liquid, and the high cost of re-vaporizing the liquid. In addition, the hazards of handling and transporting a voltatile, combustible liquid at approximately 260 F. are evident. Accordingly, more practical methods of transporting the natural gas still are being sought.

Recently, it has been proposed to convert natural gas to methanol at these distant gas producing areas, transport the methanol in conventional tankers, and then re-convert the methanol to natural gas at the point of destination. While this proposal appears to have considerable merit, the oxygen content of methanol, comprising half of its total weight, is converted on hydrogenation to water with no economic value. Possibly for this reason, and others, this method has not at the present time been commercially practiced.

Accordingly, the principal object of the present invention is to provide improved methods for transporting and/ or storing natural gas.

More particularly, it is an object to provide improved Patented Jan. 16, 1973 methods for transporting utilizable quantities or supplies of natural gas from distant gas producing areas to the United States and elsewhere.

More particularly still, it is an object to convert the natural gas to a form more easily transported, or stored, in standard atmospheric containers using a minimum of refrigeration or in low pressure vessels.

Still another object is to convert the natural gas to a form having a high percentage of carbon per unit volume than other 'forms presently transported.

Another object is to convert the natural gas to a form which upon being re-converted produces products which are all salable, or can be recycled.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The above objectives are accomplished and the disadvantages of the above-described methods of transporting natural gas are accomplished by transporting bulk volumes of natural gas in the form of a loweralkyl amine to a point remote from a point of origination, decomposing the lower alkyl amine at the point of destination to methane, ammonia and nitrogen, and then separating the methane for utilization. The lower alkyl amine can be thermally decomposed, or it can be decomposed by catalytic hydrogenation. The nitrogen content of the amine can be recycled on the return trip of the transporting vessel as aqueous ammonia for re-use, or it can be used as a hydrogen source in the reconversion of the amine to natural gas.

Preferably and advantageously, the lower alkyl amine comprises mixed lower amines, wherein each lower amine has from one to twelve carbon atoms. These amine mixtures are more desirable because of their higher boiling .points and their greater capacity for carrying carbon in a unitvolume of liquid. Furthermore, on reconversion by hydrogenation, they produce a fuel gas having a higher heat of combustion which is often desirable. In still other cases, it may be desirable to transport the natural gas in a non-volatile, solid form in which event a quaternary ammonium salt of the lower alkyl amine can be formed by reacting an acidic alkyl salt with the lower alkyl amine. Existing processes can be used to convert the natural gas to a lower alkyl amine, using a number of conversion steps, although the cost of manufacturing the amine can be reduced by decreasing the number of conversion steps and merging them into a two or possibly a one-step operation. Generally, however, a three step conversion process would include:

(1) reactin natural gas, air and steam to produce ammonia; (2) reacting natural gas and steam to produce methanol;

and

(3) then reacting the ammonia and the methanol to produce the amine mixture.

In particular, in large capacity plants, ammonia and methanol presently are manufactured by the reactions:

CH4 21120 4H2 CO2} SYNTHESIS GAS OH H20 3H2 00 PRODUCTION 0H, N; 002 H20 COMBUSTION reactions, or derived in other appropriate fashions, are used to manufacture an amine mixture by the reactions:

It can be seen that these reactions produce an amine mixture composed mainly of dimethyl' amine and dimethyl amine and trimethyl amine. Such a mixture has a normal boiling point of approximately 40 F., thus it can be easily monia is available for sale or it may be used as a hydrogen source or re-cycled as aqueous ammonia for conversion to additional amines. Using the latter manner, of course, would reduce foreign capital investment, whereas shipped or stored in standard atmospheric containers ususing it as a domestic source of hydrogen will reduce the ing a minimum of refrigeration, or in low pressure vesamount of methane consumed in the reconversion of the sels. Furthermore, it has a higher volumetric carbon conamine. Direct sale of ammonia also would greatly oiT tent than LNG, methanol or compressed gas. For examset the amine manufacturing costs and theref re would ple, in Table I below, the above, as well as other advan- Tedllfie the Cost of the methane transpcltedtages f this method, are i As indicated above, a preferred and advantageous form for transporting or storing natural gas is an amine mix- TABLE I ture r1ch in methyl amines, but also contaimng appreciable 53m $25; percentages of higher amines. Such mixtures are manu- Liquid MW 9 1 1, gal, factured by reacting mixtures of carbon monoxide, hydro- Methane (LNG) 16.04 R 259 gen, andmtrogen. These am ne mixtures are more desir- Methanol 32.04 149 6.60 2.47 able than mixed methyl amines because of their higher Dimethyl amine 45.08 45 5.67 3.02 Trimethyl amine 5M1 38 F. 3' 36 boihng points and their greater capacity for carrying car bon in a unit volume of liquid. Furthermore, as 1nd1cated Compressed gas above, on reconversion by hydrogenation, these higher Pres- Lbs, g0 amines produce a fuel gas having a higher heat of com- Temperasure carbon Gas o p.513: LbsJgaL gal bustion which is often desirable. Typical ones of these M 60 000 3 13 2 higher amines and their properties are set forth in Table 9 4 5119 1 H below.

TABLE II Melting Boiling Lb point, point, Lbs. carbon] Compound MW SG 0. C. c. c

Ethyl amine 45. 08 0.689215 -s4 16.671J 42.9 22.8 Diethyl amine- 73.14 0. 7108 4 56. 3 44.4 29.1 Trietliyl amine- 101.19 0. 7255 4 89-90 45.3 32.3 Propyl amine... 59.11 0.719 20 -s3 49 44.9 27.4 Dipropyl amine- 101.19 0.73844 46.0 32.7 0. Tripropyl amine 143.27 0.7534 156 47.0 35.4 Butyl amine-.-" 73.14 0.76-1 77. 816E 17.4 31.1 Dibutylamine- 129.25 0.7671 159 47.9 35.5 Tributylamine 185.36 0. 7782 n Z16l27 48.5 37.4

By reactin an acidic alk 1 salt or halo enated comg g It is evident that the carbon content per unit volume of trimethyl amine is far greater than any of the other liquids and is greater than 40% that of methane gas compressed to 20,000 p.s.i.a. In comparison with methanol on a carbon basis, the amine is more efiicient volumetrically by 36%.

In addition to the fact that the natural gas can be easily converted to an amine mixture and can be easily transported and/ or stored, the amine mixture can be easily re-converted or decomposed by catalytic hydrogenation to pound with the lower alkyl tertiary amine, a non-volatile, solid quaternary ammonium salt can be manufactured. These solids decompose on heating at approximately 230 C. and above. The carbon carrying capacity of these quaternaries is also very high in comparison with LNG and may approach twice that of methane. Methyl chloride or other methyl halide, methyl sulfate can be reacted with the amine mixture to form solid quaternary am- 1 monium compounds, such as those set forth in Table III below.

methane, ammonia and nitrogen, for example, by the reaction:

After separation and drying, using presently known processes, the methane can be utilized as fuel and the am- It will thus be seen that the objects set forth above,

among those made apparent from the preceding description, are efficiently attained and certain changes may be made in carrying out the above method. Accordingly, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

Now that the invention has been described, what is claimed as new and desired to be secured by Letters Patent is:

1. A method of obtaining large utilizable supplies of methane for fuel or the like, which includes the steps of transporting bulk volumes of methane in the form of a lower alkyl amine to a point remote from a point of origination, lower alkyl amine being formed by reacting ammonia with methanol derivated from said methane, decomposing said lower alkyl amine at the point of destination to methane, ammonia and nitrogen, and separating said methane for utilization.

2. A method which includes the steps of claim 1 above, wherein said lower alkyl amine is transported through a pipeline.

3. A method which includes the steps of claim 1 above,

wherein said lower alkyl amine is transported on a carrier.

4. A method which includes the steps of claim 1 above, wherein said lower alkyl amine is decomposed by catalytic hydrogenation to methane, ammonia and nitrogen.

5. A method which includes the steps of claim 1 above, wherein said alkyl amine is thermally decomposed to methane, ammonia and nitrogen.

6. A method which includes the steps of claim 1 above, wherein said lower alkyl amine comprises mixed lower alkyl amines, wherein each lower alkyl amine has from one to twelve carbon atoms.

7. A method which includes the steps of claim 6. above, wherein a major amount of the mixed lower alkyl amine comprises at least one of dimethyl amine and trimethyl amine.

8. A method which includes the steps of claim 1 above, and which further includes the steps of forming a quaternary ammonium salt of said lower alkyl amine by reacting an acidic alkyl salt with said lower alkyl amine.

9. A method which includes the steps of claim 8 above, wherein said quaternary ammonium salt is formed at the point of origination.

10. A method which includes the steps of claim 8 above, wherein said quaternary ammonium salt of the lower alkyl amine is a solid at room temperature.

11. A method which includes the steps of claim 8 above, wherein said quaternary ammonium salt is decomposed to recover methane, ammonia and nitrogen.

12. A method which includes the steps of claim 1 above, wherein said methane is present in natural gas, and a bulk volume of said natural gas is transported as heavy carbon weight alkyl amines.

13. A method which includes the steps of claim 12 above, wherein said lower alkyl amine includes a majority of at least one of dimethyl amine and trimethyl amine.

References Cited UNITED STATES PATENTS 3,514,274 5/1970 Cahn et a1. 260-676 X 2,788,265 4/1957 Bowers 48-196 R 2,958,205 11/1960 McConkey 48190 3,574,276 4/1971 Strelzofi 48--190 PAUL M. COUGHLAN, 111., Primary Examiner J. M. NELSON, Assistant Examiner U.S. Cl. X.R. 

